In last months D.O.C. I began Part I of the Packard Electromatic Clutch article. It included how it works, schematics, the components and a Troubles and Corrections chart (see www.southernwheels.com Archives section for the December 2011 article). This month I will continue with detailed descriptions of components, illustrations and adjustments.
What is an Electromatic Clutch?
It allows the driver to shift gears in the usual way, but without touching the clutch pedal; even when stopping its not necessary to touch the clutch pedal. It is operated by the cars electrical and vacuum systems and can be locked by a lock out switch on the instrument panel.
To lock out: For conventional clutch use, pull the knob out.
To bring the Electromatic clutch into operation, push the knob in
Electromatic Clutch Components
The Lockout Solenoid Valve Consisting of one winding and a core with a rubber-tipped plunger that acts as a valve, this causes a positive lockout of the control valve. A compression spring holds the core and valve in a normally-closed position, shutting off the vacuum in the clutch control valve vacuum passage, completely locking out the Electromatic Clutch (Figure 1). When the solenoid coil is energized, the core and valve plunger are pulled down, compressing the seating spring, opening the valve, subjecting the power cylinder diaphragm to partial vacuum.
The Clutch Control Valve To create a vacuum, all of the air would have to be totally pumped out of an enclosed vessel. So far, this has not been possible, so the use of the word vacuum in the following descriptions is actually meant to be partial vacuum.
The intensity of the vacuum in the engine intake manifold varies with the engine speed. At low speed, the vacuum is high and at high speed the vacuum is low. This variation is exploited by the Electromatic Clutch and its control is the work of the clutch control valve. The clutch control valve assembly consists of the valve body, a diaphragm, the spool valve and sleeve, and the accelerator linkage and fulcrum lever.
The Valve Body (Figure 2) is die-cast. It supports the moving parts of the valve and contains three chambers: vacuum passage, air inlet chamber and power cylinder chamber.
The vacuum passage is connected to the intake manifold by tubing. This passage contains the lockout solenoid valve described above, which when actuated, stops off the vacuum passage and makes the control valve inoperative.
The air inlet chamber contains the valve rod and fulcrum lever (part of the linkage operating from the throttle) and the diaphragm and shaft. It is vented to the atmosphere.
The power cylinder chamber subjects the power cylinder to either atmospheric pressure or vacuum, depending on whether the valve sleeve ports are open or closed.
The diaphragm is connected to the spool valve by the fulcrum lever, pinned to the diaphragm shaft. One side of the diaphragm is always at the same vacuum intensity as the power cylinder and this side is spring-loaded. The opposite side of the diaphragm makes up the rear wall of the air inlet chamber and is exposed only to atmospheric pressure, so the engine vacuum controls the position of the diaphragm shaft and position of the spool valve in the sleeve.
A hollow piston-type valve called the spool valve is free to slide fore and aft in the valve sleeve. Its forward motion is controlled by the linkage from the accelerator, and its movement to the rear is controlled by the diaphragm, both working through the fulcrum lever. Its purpose is to block off or open the sleeve ports, admitting either atmospheric pressure to the power cylinder or subjecting it to vacuum
The Power Cylinder This diaphragm-type power cylinder (Figure 3) provides the force required for the disengagement and the degree of engagement of the clutch. A steel reinforced, rubber fabric diaphragm separates the two chambers of the power cylinder. One of these chambers connects to the clutch control valve by means of a metal tube and is always at the degree of vacuum supplied by the control valve. The chamber on the side of the diaphragm away from the vacuum line, however, is vented to the atmosphere. A flexible steel cable attached to the center of the diaphragm travels around a pulley bolted to the clutch relay lever, and is secured at the opposite end to a bracket on the starter motor.
For clutch disengagement (Figure 4) the control valve subject the power cylinder to the full vacuum of the intake manifold. The diaphragm, through the cable pulley system, exerts upon the clutch relay lever the pull necessary to disengage the clutch.
For clutch engagement (Figure 5) the diaphragm being in the disengaged position, the control valve bleeds atmospheric pressure to the power cylinder. This allows the diaphragm to uniformly assume its relaxed position until all tension has been relieved from the cable and relay lever and the clutch is in full engagement.
The Governor Switch With only the controls described so far, the clutch would be disengaged, allowing the car to free-wheel every time the accelerator pedal was released. The centrifugally-operated governor switch is provided to prevent clutch disengagement at speeds greater than governed speed. It contains two sets of contacts: One marked EC(Electromatic Clutch) and one marked AD(formerly Aerodrive, now Overdrive). The ADcontacts are normally open below governed speeds and control the engaging mechanism of the overdrive. Both sets of contacts are operated by centrifugal force set up by rotating flyweights, which open the ECcontacts and close the ADcontacts when the car is moving above governed speeds. Opening the ECcontacts breaks the lockout solenoid ground circuit, de-energizing the solenoid, and stops off the vacuum from the power cylinder, preventing clutch disengagement above governed speeds.
The Direct Speed Switch While the governor switch is necessary to lock out the Electromatic above governed speed, it is important to have a means of overriding this switch in order to shift gears above governed speeds. Because of this, the plunger type direct speed switch, (Figure 6) has been provided. It is bracket-mounted to the engine crank case and is operated by the direct and second idler lever. Connected in parallel with the governor switch, it closes the Electromatic circuit at the first movement of the gearshift lever and, consequently, the first movement of the direct and second idler lever. When the shifting lever is moved to high gear position, the idler lever is pulled outward by the shifter linkage. This outward movement pushes in the plunger of the direct speed switch, opening its contacts and locking out the Electromatic. Any movement of the shifting lever out of high gear position moves the idler lever inward, instantly closing the direct speed contacts and making the Electromatic operative before any movement of the high gear synchronizer takes place. The direct and second idler allows the Electromatic to operated when the shifting lever is moved out high gear position at speeds above governed speed.
The Accelerator Switch. With only the controls described above, the clutch would be disengaged each time the accelerator pedal was released below governed speed. To prevent this, the accelerator switch has been provided, operated by a linkage secondary to the throttle linkage (Figure 7). It is connected in series with the governor ECcontacts and is so adjusted that the switch contacts open just as the slack in the linkage has been taken up when the accelerator is depressed. This breaks the circuit and locks out the Electromatic. When the accelerator pedal is fully released below governed speed, the adjustment of the switch is such that its contacts are closed, makingthe circuit, allowing the Electromatic to operate.
Adjusting the Electromatic Clutch
Misadjustment from the factory, as well as normal wear of mechanical parts can necessitate adjustment of the Electromatic. Any linkage will wear if put to repeated use, and since the Electromatic tolerances must be held closely for efficient operation, adjustments have been provided to compensate for reasonable slack. Before making any Electromatic adjustments, first check the clutch pedal for free play. It should be kept in mind that the Electromatic is in effect an automatic clutch pedal, and that ideal operation is impossible unless all troubles of the clutch proper have been eliminated.
Engine Speed Screw Purpose: to advance or retard the clutch cushion point (that is the RPM of the engine at which the clutch starts to engage with respect to throttle opening.
Effect: Regulates the distance the control valve piston travels before the throttle opens.
Procedure: With engine warm and at low idle, the transmission in second gear, adjust the engine speed screw (Figure 8) so that the car will just move on a level floor when the operating lever is brought up against the engine speed screw. The normal gap between engine speed screw and operating lever should be about 7/32
Valve Operating Rod Purpose: To provide additional adjustment if necessary after engine speed screw has been turned in or out to its limit. Adjustment should not be made unless engine speed screw adjustment is not adequate.
Effect: When engine speed screw travel is not sufficient, the valve operating rod regulates the distance the control valve piston travels before throttle opens.
Procedure: With engine warm, at low idle, transmission in neutral, hold throttle operating lever against the bracket stop. Move the valve operating lever until there is 1/8gap between lever and stop, and hold lever in this position. Move valve rod in slowly until power cylinder operating cable just starts to move on the clutch release stroke. Hold valve rod at this point and adjust valve rod clevis (Figure 9) until valve operating link will go into position. Connect valve operating link and fasten it with spring clip lock.
We will conclude next month with electrical testing and servicing of the Electromatic Clutch. All of us at Southern Wheels wish you and your families a Merry Christmas. Lets work together to make 2012 a strong and prosperous year! Keep em driving!